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Abstract:

A diagnostic circuit for trouble shooting electronic control units of
appliances includes a voltage sensing and signal generation device with
an input/output and an input. The circuit includes first terminals for
connecting to the load and second terminals for connecting to the two
lines of the sinusoidal source. One of the first terminals is connected
to the input/output, and another one of the first terminals is connected
to the input. A relay is connected between one of the second terminals
and the input/output. Another relay is connected between another one of
the second terminals and the input. A first diode pair with clamping
diodes is connected to the input/output, and a second diode pair first
diode pair with clamping diodes is connected to the input.

Claims:

1. A diagnostic circuit for connecting to a unit under test having a load
and two lines of a sinusoidal source, the diagnostic circuit comprising:
a voltage sensing and signal generation device having an input/output and
an input; a plurality of terminals including first terminals for
connecting to the load and second terminals for connecting to the two
lines of the sinusoidal source, one of said first terminals connected to
said input/output, and another one of said first terminals connected to
said input; a plurality of relays, one of said plurality of relays
connected between one of said second terminals and said input/output, and
another one of said plurality of relays connected between another one of
said second terminals and said input; a D/C voltage source and ground; a
first diode pair having a first clamping diode connected between said D/C
voltage source and said input/output and a second clamping diode
connected between said ground and said input/output; and a second diode
pair having a first clamping diode connected between said D/C voltage
source and said input and a second clamping diode connected between said
ground and said input.

2. The diagnostic circuit according to claim 1, further comprising: a
first capacitor connected between said input/output and said ground; and
a second capacitor connected between said input and said ground.

3. The diagnostic circuit according to claim 1, further comprising: at
least one first resistor connected between said input/output and a first
one of said first terminals for limiting a current sensed at said
input/output; and at least one second resistor connected between said
input and a second one of said first terminals for limiting a current
sensed at said input.

4. The diagnostic circuit according to claim 1, further comprising: a
first pull-down resistor connected between said input/output and said
ground; and a second pull-down resistor connected between said input and
said ground.

5. The diagnostic circuit according to claim 1, further comprising: a
first isolation capacitor connected between said input/output and a first
one of said first terminals; a second isolation capacitor connected
between said input and a second one of said first terminals; and a third
isolation capacitor for connection between neutral and DC ground.

6. The diagnostic circuit according to claim 1, wherein: said voltage
sensing and signal generation device has a first operating mode in which
said input/output of said voltage sensing and signal generation device is
an output, and a second operating mode in which said input/output of said
voltage sensing and signal generation device is an input.

7. The diagnostic circuit according to claim 1, further comprising: an
additional terminal for connecting to an additional load, said voltage
sensing and signal generation device having a further input connected to
said additional terminal; a further terminal for connecting to one of the
two lines of the sinusoidal source; a further relay connected between
said further terminal and said further input; and a third diode pair
having a first clamping diode connected between said D/C voltage source
and said further input and a second clamping diode connected between said
ground and said further input.

8. The diagnostic circuit according to claim 7, further comprising: a
pull-down resistor connected between said further input and said ground;
a capacitor connected between said further input and said ground; at
least one resistor connected between said further input and said
additional terminal; and an isolation capacitor connected between said
further input and said additional terminal.

9. A diagnostic circuit for connecting to a unit under test having a load
and a sinusoidal source, the diagnostic circuit comprising: a voltage
sensing and signal generation device having an input for sensing a signal
and an output for providing a signal; a first terminal for connecting to
the load and a second terminal for connecting to the sinusoidal source; a
relay connected between said second terminal and said input; a D/C
voltage source and ground; a first diode pair having a first clamping
diode connected between said D/C voltage source and said input and a
second clamping diode connected between said ground and said input; and a
second diode pair having a first clamping diode connected between said
D/C voltage source and said input/output and a second clamping diode
connected between said ground and said input/output.

10. The diagnostic circuit according to claim 9, further comprising: a
pull-down resistor connected between said input and said ground; a
capacitor connected between said input and said ground; at least one
resistor connected between said input and said first terminal; an
isolation capacitor connected between said input and said first terminal;
an isolation capacitor connected between said output and said first
terminal; and an isolation capacitor for connection between neutral and
DC ground.

11. A diagnostic circuit for connecting to a unit under test having a
load and a sinusoidal source, the diagnostic circuit comprising: a
voltage sensing and signal generation device having a first input, a
second input, and an output; a plurality of first terminals, each one of
said plurality of first terminals for connecting to a respective one of a
plurality of loads; a plurality of second terminals for connecting to the
sinusoidal source; a plurality of relays each connected between a
respective one of said plurality of second terminals and a respective one
of said plurality of first terminals; a D/C voltage source and ground; a
first diode pair having a first clamping diode connected between said D/C
voltage source and said first input and a second clamping diode connected
between said ground and said first input; a second diode pair having a
first clamping diode connected between said D/C voltage source and said
second input and a second clamping diode connected between said ground
and said second input; and a third diode pair having a first clamping
diode connected between said D/C voltage source and said output and a
second clamping diode connected between said ground and said output.

12. The diagnostic circuit according to claim 11, further comprising: a
first resistor connected between said output and said third diode pair; a
second resistor connected to said output; and a fourth diode pair having
a first clamping diode connected between said D/C voltage source and said
second resistor and a second clamping diode connected between said ground
and said second resistor.

13. The diagnostic circuit according to claim 11, further comprising: at
least one resistor and an isolation capacitor connected in series between
said first input and a first one of said plurality of first terminals; at
least one resistor and an isolation capacitor connected in series between
said second input and a second one of said plurality of first terminals;
at least one resistor and an isolation capacitor connected in series
between said output and said first one of said plurality of first
terminals; at least one resistor and an isolation capacitor connected in
series between said output and said first one of said plurality of first
terminals; and an isolation capacitor for connection between neutral and
DC ground.

14. The diagnostic circuit according to claim 11, further comprising: at
least one resistor and an isolation capacitor connected in series between
said first input and a first one of said plurality of first terminals; at
least one resistor and an isolation capacitor connected in series between
said second input and a second one of said plurality of first terminals;
an amplifier having an input connected to said output, said amplifier
having an output; at least one resistor and an isolation capacitor
connected in series between said output of said amplifier and said first
one of said plurality of first terminals; at least one resistor and an
isolation capacitor connected in series between said output of said
amplifier and said first one of said plurality of first terminals; and an
isolation capacitor for connection between neutral and DC ground.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation-in-part application of application Ser. No.
13/166,299, filed Jun. 22, 2011, which is a divisional application of
application Ser. No. 12/039,209, filed Feb. 28, 2008; the prior
applications are herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a diagnostic circuit and more specifically
to a diagnostic circuit for trouble shooting electronic control units of
appliances.

[0004] 2. Description of the Related Art

[0005] Current sensing diagnostic circuits are often used in appliances
(e.g. refrigerators) to monitor the operation of electrical components
such as, for example, control units of the appliance. During testing, a
current should flow when a controlled relay is commanded to close, and a
sensor detects that current and reports that the electrical component
being tested is operating as intended. If, however, current does not flow
through the diagnostic circuit when the relay is commanded to close, the
sensor notes the absence of that current and reports to a controller
(e.g. microprocessor) that the electrical component is not functioning
properly. When the electrical component is not working, malfunctioning,
and the like, a technician is often summoned to repair and/or replace the
electrical component in the appliance. Unfortunately, an indication of a
failure of the electrical component to function properly can occur when a
variety of different faults (e.g. an open load, a disconnected wire, and
the like) are experienced and/or the electrical component itself is
damaged. Therefore, the technician will have to check a number of
different potential problems to determine which electrical component has
actually failed, which electrical component needs to be replaced, which
leads or connections to check, and the like.

[0006] Often a current transformer is used in the diagnostic circuit for
supplying the current. However, the dynamic range of currents in modern
appliances is 10 mA to 25 A. Such a wide range of currents is difficult
to produce using a current transformer and requires multiple current
transformers leading to a complex diagnostic circuit. In addition,
current sensing cannot differentiate between an open load and a defective
load.

[0007] It is a well-known problem that service technicians have a tendency
to automatically replace electronic control units when repairing an
appliance. Unfortunately, most of the replaced electronic control units
are not defective. There is a need to provide a simple, low cost
diagnostic circuit that proves that the control unit is functioning
properly and that problems are most likely not related to the electronic
control unit.

BRIEF SUMMARY OF THE INVENTION

[0008] It is accordingly an object of the invention to provide a
diagnostic circuit and a method of testing a circuit that overcomes the
above-mentioned disadvantages of the prior art device and methods of this
general type, which provides an inexpensive yet effective diagnostic test
device for testing control units.

[0009] With the foregoing and other objects in view there is provided, in
accordance with the invention, a diagnostic circuit for connecting to a
unit under test that has a load and a sinusoidal source. The diagnostic
circuit includes a voltage sensing device with an input for sensing a
signal, a first terminal for connecting to the load, a second terminal
for connecting to the sinusoidal source, and a relay connected between
the first and second terminals for connecting the sinusoidal source to
the load. Clamping diodes are provided and include a first clamping diode
connected between a D/C voltage source and the input and a second
clamping diode connected between the ground and the input. A resistor is
connected between the D/C voltage source and the first terminal.

[0010] In accordance with an added feature of the invention, a capacitor
is connected between the input and ground for filtering the signals. At
least one further resistor is connected between the input and the first
terminal for limiting a current sensed at the input.

[0011] In accordance with another feature of the invention, the voltage
sensing device is a micro-controlled analog-to-digital converter circuit.

[0012] With the foregoing and other objects in view there is further
provided, in accordance with the invention, a diagnostic circuit for
connecting to a unit under test having a load and two lines of a
sinusoidal source. The diagnostic circuit includes a voltage sensing
device having a first input and a second input, terminals including first
terminals for connecting to the load and second terminals for connecting
to the two lines of the sinusoidal source, relays each connected between
one of the second terminals and one of the first terminals for connecting
the sinusoidal source to the load, and a first diode pair having a first
clamping diode connected between a D/C voltage source and the first input
and a second clamping diode connected between ground and the first input.
A second diode pair is provided and has a first clamping diode connected
between the D/C voltage source and the second input and a second clamping
diode connected between ground and the second input.

[0013] In accordance with an additional feature the invention, a first
capacitor is connected between the first input and ground, and a second
capacitor is connected between the second input and ground. Ideally, at
least one first resistor is connected between the first input and a first
one of the first terminals for limiting a current sensed at the first
input. Furthermore, at least one second resistor is connected between the
second input and a second one of the first terminals for limiting a
current sensed at the second input. A first pull-down resistor is
connected between the first input and ground, and a second pull-down
resistor is connected between the second input and ground.

[0014] With the foregoing and other objects in view there is further
provided, in accordance with the invention, a diagnostic circuit for
connecting to a unit under test having a load and a sinusoidal source.
The diagnostic circuit includes a voltage sensing device having an input
for sensing a signal, terminals including first terminals for connecting
to the load and a second terminal for connecting to the sinusoidal
source, a relay connected between one of the first terminals and the
second terminal for connecting the sinusoidal source to the load, and
clamping diodes including a first clamping diode connected between a D/C
voltage source and the input and a second clamping diode connected
between ground and the input. In this embodiment, a first capacitor is
connected between ground and a first one of the first terminals, and a
second capacitor is connected between the clamping diodes and a second
one of the first terminals.

[0015] In accordance with a further feature of the invention, at least one
resistor is connected between the input and one of the first and second
capacitors.

[0016] With the foregoing and other objects in view there is additionally
provided, in accordance with the invention, a diagnostic circuit for
connecting to a unit under test having a load and a sinusoidal source.
The diagnostic circuit contains a voltage sensing device having a first
input for sensing a signal and a second input, terminals including a
first terminal for connecting to the load and a second terminal for
connecting to the sinusoidal source, a relay connected between the first
terminal and the second terminal for connecting the sinusoidal source to
the load, and clamping diodes including a first clamping diode connected
between a D/C voltage source and the input and a second clamping diode
connected between ground and the input. A first capacitor is connected
between the first terminal and the first input and a second capacitor
connected between the second terminal and the second input.

[0017] In accordance with another added feature of the invention, at least
one resistor is connected between the first input and the first
capacitor.

[0018] With the foregoing and other objects in view there is additionally
provided, in accordance with the invention, a diagnostic circuit for
connecting to a unit under test having a load and three lines of a
sinusoidal source. The diagnostic circuit contains a voltage sensing
device having a first input and a second input, terminals including first
terminals for connecting to the load and second terminals for connecting
to two lines of the sinusoidal source, relays each connected between one
of the second terminals and one of the first terminals for connecting the
sinusoidal source to the load, a first diode pair having a first clamping
diode connected between a D/C voltage source and the first input and a
second clamping diode connected between ground and the first input, and a
second diode pair having a first clamping diode connected between the D/C
voltage source and the second input and a second clamping diode connected
between ground and the second input. A first capacitor is connected
between a first of the first terminals and the first input; and a second
capacitor is connected between a second of the first terminals and the
second input.

[0019] In accordance with a further feature of the invention, a third
capacitor is connected between a third line of the sinusoidal source and
the ground.

[0020] In accordance with another feature of the invention, at least one
resistor is connected between the first input and the first capacitor.
Preferably, at least one resistor is connected between the second input
and the second capacitor.

[0021] With the foregoing and other objects in view there is additionally
provided, in accordance with the invention, a method for testing a
circuit. The method includes the steps of connecting a diagnostic test
circuit to a load terminal of the circuit and to a line of a sinusoidal
source of the circuit; maintaining a relay connected between the load
terminal and the line in an open position; sensing a first voltage signal
at a sensing node coupled to the load terminal; deriving an operational
condition of the circuit in dependence on the first voltage signal
sensed.

[0022] In accordance with an added mode of the invention, there are the
further steps of switching the relay to a closed position for connecting
the load to the sinusoidal source; sensing a second voltage signal at the
sensing node; and deriving the operational condition of the circuit in
dependence on the second voltage signal sensed. The circuit is considered
to be error free if the first voltage signal is less than 4 V D/C and
that the second voltage signal is an oscillating signal. The circuit is
considered to be defective if the first voltage signal is greater than
4.5 V D/C or no oscillating signal is detected.

[0023] With the foregoing and other objects in view there is provided, in
accordance with the invention, a method for testing a circuit. The method
includes the steps of connecting a diagnostic tester to a load terminal
of the circuit and to two lines of a multi-phase sinusoidal source of the
circuit; maintaining a first relay, of the diagnostic tester, connected
between a first load terminal and a first line in an open position;
maintaining a second relay, of the diagnostic tester, connected between a
second load terminal and a second line in an open position; sensing a
first voltage signal at a first sensing node coupled to the first load
terminal; sensing a second voltage signal at a second sensing node
coupled to the second load terminal; and deriving an operational
condition of the circuit in dependence on the first and second voltage
signals sensed.

[0024] In accordance with an added mode of the invention, there are the
further steps of switching the first relay to a closed position for
connecting the load to a first line of the multiphase sinusoidal source;
sensing a third voltage signal at the first sensing node; sensing a
fourth voltage signal at the second sensing node; and deriving the
operational condition of the circuit in dependence on the third and
fourth voltage signals sensed.

[0025] In accordance with a further mode of the invention, there are the
further steps of switching the first relay to an opened position;
switching the second relay to a closed position for connecting the load
to a second line of the multiphase sinusoidal source; sensing a fifth
voltage signal at the first sensing node; sensing a sixth voltage signal
at the second sensing node; and deriving the operational condition of the
circuit in dependence on the fifth and sixth voltage signals sensed.

[0026] In accordance with another added mode of the invention, there are
the further steps of switching the first relay to a closed position;
maintaining the second relay at the closed position; sensing a seventh
voltage signal at the first sensing node; sensing an eighth voltage
signal at the second sensing node; and deriving the operational condition
of the circuit in dependence on the seventh and eighth voltage signals
sensed.

[0027] The circuit is considered error free if the first and second
voltage signals are logic low. The circuit is considered error free if
the third and fourth voltage signals are oscillating signals having the
same phase. The circuit is considered error free if the fifth and sixth
voltage signals are oscillating signals having the same phase. The
circuit is considered error free if the seventh and eighth voltage
signals are oscillating signals having different phases.

[0028] With the foregoing and other objects in view there is provided, in
accordance with the invention, a diagnostic circuit for connecting to a
unit under test having a load and two lines of a sinusoidal source. The
diagnostic circuit includes a voltage sensing and signal generation
device having an input/output and an input. The diagnostic circuit
includes a plurality of terminals including first terminals for
connecting to the load and second terminals for connecting to the two
lines of the sinusoidal source. One of the first terminals is connected
to the input/output, and another one of the first terminals is connected
to the input. The diagnostic circuit includes a plurality of relays. One
of the plurality of relays is connected between one of the second
terminals and the input/output. Another one of the plurality of relays is
connected between another one of the second terminals and the input. The
diagnostic circuit includes a D/C voltage source and ground. The
diagnostic circuit includes a first diode pair having a first clamping
diode connected between the D/C voltage source and the input/output and a
second clamping diode connected between the ground and the input/output.
The diagnostic circuit also includes a second diode pair having a first
clamping diode connected between the D/C voltage source and the input and
a second clamping diode connected between the ground and the input.

[0029] In accordance with another feature of the invention, a first
capacitor is connected between the input/output and the ground; and a
second capacitor is connected between the input and the ground.

[0030] In accordance with another added feature of the invention, at least
one first resistor is connected between the input/output and a first one
of the first terminals for limiting a current sensed at the input/output;
and at least one second resistor is connected between the input and a
second one of the first terminals for limiting a current sensed at the
input.

[0031] In accordance with another feature of the invention, a first
pull-down resistor is connected between the input/output and the ground;
and a second pull-down resistor is connected between the input and the
ground.

[0032] In accordance with another added feature of the invention, a first
isolation capacitor is connected between the input/output and a first one
of the first terminals; a second isolation capacitor is connected between
the input and a second one of the first terminals; and a third isolation
capacitor is provided for connection between neutral and DC ground.

[0033] In accordance with another feature of the invention, the voltage
sensing and signal generation device has a first operating mode in which
the input/output of the voltage sensing and signal generation device is
an output, and a second operating mode in which the input/output of the
voltage sensing and signal generation device is an input.

[0034] In accordance with another added feature of the invention, the
circuit has an additional terminal for connecting to an additional load,
and the voltage sensing and signal generation device has a further input
connected to the additional terminal; the circuit has a further terminal
for connecting to one of the two lines of the sinusoidal source; the
circuit has a further relay connected between the further terminal and
the further input; and the circuit has a third diode pair having a first
clamping diode connected between the D/C voltage source and the further
input and a second clamping diode connected between the ground and the
further input.

[0035] In accordance with another feature of the invention, a pull-down
resistor is connected between the further input and the ground; a
capacitor is connected between the further input and the ground; at least
one resistor is connected between the further input and the additional
terminal; and an isolation capacitor is connected between the further
input and the additional terminal.

[0036] With the foregoing and other objects in view there is provided, in
accordance with the invention, a diagnostic circuit for connecting to a
unit under test having a load and a sinusoidal source. The diagnostic
circuit includes a voltage sensing and signal generation device having an
input for sensing a signal and an output for providing a signal. The
diagnostic circuit includes a first terminal for connecting to the load
and a second terminal for connecting to the sinusoidal source. The
diagnostic circuit includes a relay connected between the second terminal
and the input. The diagnostic circuit includes a D/C voltage source and
ground. The diagnostic circuit includes a first diode pair having a first
clamping diode connected between the D/C voltage source and the input and
a second clamping diode connected between the ground and the input. The
diagnostic circuit includes a second diode pair having a first clamping
diode connected between the D/C voltage source and the input/output and a
second clamping diode connected between the ground and the input/output.

[0037] In accordance with another feature of the invention, a pull-down
resistor is connected between the input and the ground; a capacitor is
connected between the input and the ground; at least one resistor is
connected between the input and the first terminal; an isolation
capacitor is connected between the input and the first terminal; an
isolation capacitor is connected between the output and the first
terminal; and an isolation capacitor is provided for connection between
neutral and DC ground.

[0038] With the foregoing and other objects in view there is provided, in
accordance with the invention, a diagnostic circuit for connecting to a
unit under test having a load and a sinusoidal source. The diagnostic
circuit includes a voltage sensing and signal generation device having a
first input, a second input, and an output. The diagnostic circuit
includes a plurality of first terminals. Each one of the plurality of
first terminals is for connecting to a respective one of a plurality of
loads. The diagnostic circuit includes a plurality of second terminals
for connecting to the sinusoidal source. The diagnostic circuit includes
a plurality of relays each connected between a respective one of the
plurality of second terminals and a respective one of the plurality of
first terminals. The diagnostic circuit includes a D/C voltage source and
ground. The diagnostic circuit includes a first diode pair having a first
clamping diode connected between the D/C voltage source and the first
input and a second clamping diode connected between the ground and the
first input. The diagnostic circuit includes a second diode pair having a
first clamping diode connected between the D/C voltage source and the
second input and a second clamping diode connected between the ground and
the second input. The diagnostic circuit includes a third diode pair
having a first clamping diode connected between the D/C voltage source
and the output and a second clamping diode connected between the ground
and the output.

[0039] In accordance with another feature of the invention, a first
resistor is connected between the output and the third diode pair; a
second resistor is connected to the output; and there is provided a
fourth diode pair having a first clamping diode connected between the D/C
voltage source and the second resistor and a second clamping diode
connected between the ground and the second resistor.

[0040] In accordance with another added feature of the invention, at least
one resistor and an isolation capacitor are connected in series between
the first input and a first one of the plurality of first terminals; at
least one resistor and an isolation capacitor are connected in series
between the second input and a second one of the plurality of first
terminals; at least one resistor and an isolation capacitor are connected
in series between the output and the first one of the plurality of first
terminals; at least one resistor and an isolation capacitor are connected
in series between the output and the first one of the plurality of first
terminals; and an isolation capacitor is provided for connection between
neutral and DC ground.

[0041] In accordance with another feature of the invention, at least one
resistor and an isolation capacitor are connected in series between the
first input and a first one of the plurality of first terminals; at least
one resistor and an isolation capacitor are connected in series between
the second input and a second one of the plurality of first terminals; an
amplifier having an input is connected to the output, the amplifier
having an output; at least one resistor and an isolation capacitor are
connected in series between the output of the amplifier and the first one
of the plurality of first terminals; at least one resistor and an
isolation capacitor are connected in series between the output of the
amplifier and the first one of the plurality of first terminals; and an
isolation capacitor is provided for connection between neutral and DC
ground.

[0042] Other features which are considered as characteristic for the
invention are set forth in the appended claims.

[0043] Although the invention is illustrated and described herein as
embodied in a diagnostic circuit and a method of testing a circuit, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and range
of equivalents of the claims.

[0044] The construction of the invention, however, together with
additional objects and advantages thereof will be best understood from
the following description of the specific embodiment when read in
connection with the accompanying drawings.

[0047]FIG. 3 is a schematic diagram of a first embodiment of a diagnostic
circuit according to the invention;

[0048]FIG. 4 is a schematic diagram of a second embodiment of the
diagnostic circuit according to the invention;

[0049] FIGS. 5-8 are schematic diagrams of a third embodiment of the
diagnostic circuit according to the invention;

[0050]FIG. 9 is a schematic diagram of a fourth embodiment of the
diagnostic circuit according to the invention; and

[0051] FIGS. 10-15 are schematic diagrams showing additional embodiments
of the diagnostic circuit according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0052] Referring now to the figures of the drawing in detail and first,
particularly, to FIG. 1 thereof, there is shown a basic circuit which
shows a connection from logic ground of a micro-controlled A/D device
MICRO to neutral N of a mains power supply. An operational equivalent
schematic circuit with the addition of a relay RELAY is shown in FIG. 2
for testing a proper connection to a load LOAD with the return to neutral
N traversing through the D/C circuit ground. With the relay RELAY open a
simple voltage divider network is formed with the voltage being read at
an input IN of the A/D device being a voltage sensing device. Table I
shows the expected voltage readings in dependence on the ohmic resistance
of the load.

[0053] Based on the voltages observed one can make conclusions about the
operational functionality of the load such as a control device of an
appliance.

[0054]FIG. 3 shows a first embodiment of a diagnostic circuit according
to the invention following the basic concepts taught in FIGS. 1 and 2
that is ideally suited for lower current loads typically energized by 120
V A/C. In FIG. 3, a filter capacitor C1 is provided for filtering noise.
Clamping diodes D1 and D2 are provided for clamping A/C voltages and
turning A/C sinusoidal signals into a square wave clamped between 0 and 5
volts. Voltage and current limiting resistors R1, R2, R3 protect the
circuit from high currents. Resistors R4 and R5 are provided for current
limiting and redundancy. Resistor R6 is also provided for current
limiting. The load LOAD represents a control unit of an appliance or the
unit under test. Three connection points A, B and C are shown, two
connection points A and B are for connecting the diagnostic circuit to
the appliance, specifically an A/C source line L1 and the load LOAD. An
internal connection C is the connection to A/C neutral N. The diagnostic
circuit measures all readings at the input IN for determining test
results. The following table now defines the operation of the diagnostic
test circuit when it is hooked up for eight different diagnostic results.
In Table II it is assumed that the load LOAD is less than 300 K ohms. Of
course it goes without saying that the value of the resistors shown in
FIG. 3 is dependent of the value of the load LOAD.

[0055] Rows 1 and 2 show conditions in which everything is working
properly and no errors are detected. Row 3 shows the condition in which
the relay RELAY of the diagnostic test circuit is detected as faulty
(e.g. stuck closed). Row 4 shows the condition where the line L1 is
faulty (open) but it is not diagnosed until the conditions in row 5 are
performed. In row 5 a 60 Hz square wave was anticipated but a D/C voltage
level is detected. Row 6 shows the conditions from determining a load
failure or an internal connection to neutral N failure because a 60 Hz
square wave was expected but only a D/C voltage reading was measured. In
row 7 the error is not detected.

[0056] For controlling more than one load, the circuit in FIG. 3 can be
repeated for each additional load.

[0057]FIG. 4 shows a second embodiment of the diagnostic circuit in which
loads LOAD 1 and LOAD 2 can be multiplexed and in which only one
micro-controlled A/D device MICRO is needed. In addition, for simplicity
FIG. 4 omits protective devices such as current and/or voltage limiting
resistors and capacitive filters. In FIG. 4, two pull-up resistors R10,
R12 are connected between a respective load LOAD 1, LOAD 2 and a 5 volts
source. Between each load LOAD 1, LOAD 2 and the one micro-controlled A/D
device MICRO is a resistor R11, R13, respectively. Table III shows the
expected voltage results to be seen at the input IN.

[0058] From Table III it is easy to ascertain voltage ranges to determine
pass and fail criteria for the loads. For example, a voltage greater than
4.5 volts indicates that both loads failed, a voltage in the range of 1.9
to 2.3 volts indicates that both loads passed, a voltage below 1.9 volts
indicates that LOAD 2 failed, and a voltage in the range of 2.3 to 3.0
volts indicates that LOAD 1 failed. Of course the ranges are load
dependent.

[0059]FIG. 5 shows a third embodiment of a simplified diagnostic circuit
suited for higher current loads typically energized by 240 V A/C such as
heater loads. The test circuit of FIG. 5 is ideally suited for sensing
high current, lower ohm loads connected to a 240 V A/C source. In FIG. 5,
the diagnostic circuit has connection points E, F, G and H for connecting
to the load LOAD and to the A/C lines L1 and L2 of the appliance under
test. Two relays RELAY 2 and RELAY 3 connect the A/C lines L1 and L2 to
the load LOAD. Two pull down resistors R20 and R21 connect the load to
ground. As in FIG. 1, the power connections are configured such that D/C
ground equals or is connected to A/C neutral N (e.g. a common ground).
The micro-controlled A/D device in this instance has two inputs IN1 and
IN2. The pull down resistors R20 and R21 connected to the inputs IN1 and
IN2 ensure a low reading with no connections. It is further noted that a
digital input can be used in place of the A/D inputs. In FIG. 5 it is
assumed that the load LOAD is between 15-20 ohms meaning that the current
is in the 10-16 amp range for 240 V A/C.

[0060] The diagnostic circuit shown in FIG. 6 is based on FIG. 5 but has
incorporated protection circuitry, filtering circuitry and clamping
circuitry. More specifically filtering capacitors C2 and C3, current
limiting resistors R22-R27 and clamping diodes D3-D6 have been added and
are functionally similarly to the same components shown in FIG. 3.

[0061] FIGS. 7 and 8 are simplified versions of FIG. 6 with only the
clamping and currently limiting circuitry shown for clarity. As shown in
FIG. 7, the A/C signal is provided by the line L1 to the relay RELAY 2
and conducted to the inputs IN1 and IN2 in which the sinusoidal signal is
clamped by the diode pairs D5, D6 and D3, D4 respectively resulting in
the shown square wave of 0 to 5 V (see FIG. 8).

[0062]FIG. 8 shows the same sinusoidal signal conducted by line L2 into
relay RELAY 3 to the inputs IN1 and IN2. The sinusoidal signal on line L2
being 180° out of phase compared to the sinusoidal signal on line
L1 for a two-phase sinusoidal source.

[0063] Table IV shows the operating states and expected results for the
circuit shown in FIG. 6.

[0064] Group A shows the four conditions of a properly functioning load
and wiring with no errors detected.

[0065] Group B shows the error detected when line L1 is disconnected.
However, we are not sure whether it is a line L1 connection error or a
relay RELAY 2 error. It is generally assumed that it is the line L1
connection as the diagnostic circuit is periodically checked.

[0066] Group C shows the error detected when line L2 is disconnected. As
stated above, we are not sure whether it is the line L2 connection error
or a relay RELAY 3 error. It is assumed to be a line L2 error.

[0067] Group D shows the error when the load LOAD is not properly
connected.

[0068] Group E shows the case when relay RELAY 2 is stuck closed when it
should be open.

[0069] Group F shows the case when relay RELAY 3 is stuck closed when it
should be open.

[0070]FIG. 9 illustrates a fourth embodiment of the diagnostic circuit.
FIG. 9 shows a capacitively isolated diagnostic test circuit for a three
phase, 240 V A/C signal. Terminals N, P, Q and R supply connection points
to the unit under test for connecting lines L1, L2 to relays RELAY 6 and
RELAY 7 respectively and to the load LOAD. Isolation capacitors C40, C41,
and C42 isolate the lines L1, L2 and neutral N from the rest of the
circuit. Current protection resistors R40-R45 are provided as are the
clamping diode sets D20, D21 and D22, D23 for protecting the
micro-controlled A/D device MICRO from harmful high-level currents and
voltages. FIG. 9 further shows a reference clock driven by line L1.

[0071] Table V shows the expected results for a properly operating load
and relay and further identifies various errors.

[0072] Rows 1-4 show the various connection configurations for a properly
operating load and relays and the expected results at the inputs IN 1 and
IN 2. Row 5 is the case where the line L1 is disconnected but this error
is not detected until the configuration of row 6 is set up and a square
wave is expected but only a logic low signal is detected. Row 7 is the
case where the line L2 is disconnected but this error is not detected
until the circuit configuration of row 8 is set up and a square wave is
expected but only a logic low signal is detected. Row 9 is the case where
the load LOAD is disconnected but the disconnection is not diagnosed
until the circuit conditions of either row 10 or 11 are performed and
logic low conditions are detected at one of the inputs.

[0073] FIG. 10 shows an embodiment of a diagnostic circuit for testing a
non-isolated 220/230 V load. The diagnostic circuit shown in FIG. 10 is
based on that shown in FIG. 6. Since basically the same components are
present, most of the reference characters used to identify the components
in FIG. 10 are the same as in FIG. 6. However, the circuit in FIG. 10
differs from the circuit in FIG. 6 in that the circuit in FIG. 10 has a
voltage sensing and signal generation device MICRO2 which includes both a
micro-controlled A/D device and a signal generation device for generating
a signal. The voltage sensing and signal generation device MICRO2
includes an input IN for receiving an input signal applied thereto and
for providing that input signal to the micro-controlled A/D device of the
voltage sensing and signal generation device MICRO2. The voltage sensing
and signal generation device MICRO2 also includes an input/output IN/OUT
that can be configured as an output when desired and that can also be
configured as an input at other desired times.

[0074] The voltage sensing and signal generation device MICRO2 has an
operating mode in which the input/output IN/OUT is configured to function
as an output and the output signal generated by the signal generation
device of the voltage sensing and signal generation device MICRO2 is
output at the input/output IN/OUT. In the operating mode in which the
input/output IN/OUT is configured to function as an output, a signal,
preferably, a pulse train of a predetermined frequency is generated by
the signal generation device of the voltage sensing and signal generation
device MICRO2 and is output at the input/output IN/OUT of the voltage
sensing and signal generation device MICRO2.

[0075] The voltage sensing and signal generation device MICRO2 also has an
operating mode in which the input/output IN/OUT is configured to function
as an input and an input signal applied to the input/output IN/OUT is
input into the micro-controlled A/D device of the voltage sensing and
signal generation device MICRO2.

[0076] The input/output IN/OUT could be implemented using a single pin or
contact that extends externally from the voltage sensing and signal
generation device MICRO2. However, it may also be possible to provide one
pin or external contact that serves as the input and to provide another
pin or external contact that serves as the output. These two pins or
contacts could then be connected together at a node external to the
voltage sensing and signal generation device MICRO2.

[0077] The diagnostic circuit has terminals or connection points F and G
for connecting to the load LOAD and has terminals or connection points E
and H for connecting to the A/C lines L1 and L2 of the appliance under
test.

[0078] To sense whether the load LOAD is connected, instead of turning on
Relay 2 and Relay 3 (as would be done in some of the previously described
embodiments), Relay 2 and Relay 3 are left open, and the voltage sensing
and signal generation device MICRO2 is set to the operating mode in which
a signal, preferably, a pulse train of a predetermined frequency is
output at the input/output IN/OUT of the voltage sensing and signal
generation device MICRO2. The predetermined frequency of the pulse train
that is output at the input/output IN/OUT is relatively high compared to
the frequency (typically 60 HZ in the US or 50 HZ in Europe) of the AC
line voltage available at lines L1 and L2. For example, the predetermined
frequency of the pulse train that is output at the input/output IN/OUT
can be set to 10 kHZ. As another example, the predetermined frequency of
the pulse train that is output at the input/output IN/OUT can be set to 1
kHZ. A load LOAD with an impedance of, for example, 10 or 20 ohms will
allow a pulse train of 1 kHZ to pass therethrough without causing any
significant heating. The signal that is input at the separate input IN
shown at the lower side of the voltage sensing and signal generation
device MICRO2 enables the micro-controlled A/D device MICRO of the
voltage sensing and signal generation device MICRO2 to detect the load
LOAD by either sensing the pulse train output by the input/output IN/OUT
or by sensing a change of the voltage across the capacitor C3 of about
0.5 Vcc. The chosen values of R21 and C3 will depend on the frequency of
the output pulse train and on the method of detecting the load LOAD.
After the load LOAD is detected, the operating mode of the voltage
sensing and signal generation device MICRO2 is changed such that the
input/output IN/OUT is turned back to an input and the AC line voltage
input at lines L1 and L2 is sensed as has been explained with reference
to the circuit shown in FIG. 6 and Table IV.

[0079] For example, when the predetermined frequency of the pulse train
that is output at the input/output IN/OUT is 10 kHZ, example component
values could be as follows: R20=R21=47 k ohms,
R22=R23=1 k ohms, R24=R25=R26=R27=100 k
ohms, and C2=C3=0.001 μF. Of course, it should be understood
that many other different combinations of component values could be used.

[0080] FIG. 11 is a schematic diagram of another embodiment of the
diagnostic circuit. The circuit shown in FIG. 11 is constructed similarly
to the circuit shown in FIG. 10 and is operated similarly to that
circuit. However, the circuit shown in FIG. 11 has additionally been
provided with isolation capacitors C100 and C101 that serve to
isolate the circuitry shown to the left of the isolation capacitors
C100 and C101 from the circuitry shown to the right of the
isolation capacitors C100 and C101. Also, an isolation
capacitor C102 is connected between neutral N of the appliance under
test and DC ground. For example, the diagnostic circuit could have a
terminal with one end of the isolation capacitor C102 connected
thereto and the other end of the isolation capacitor C102 connected
to DC ground. That terminal would then be connected to the neutral N of
the appliance under test to thereby connect one end of the isolation
capacitor C102 to neutral N of the appliance under test.

[0081] Once again, the load LOAD is sensed without closing either Relay 2
or Relay 3, and the voltage sensing and signal generation device MICRO2
is set to the operating mode in which the pulse train of the
predetermined frequency is output at the input/output IN/OUT of the
voltage sensing and signal generation device MICRO2. After the load LOAD
is seen, the operating mode of the voltage sensing and signal generation
device MICRO2 is set such that the input/output IN/OUT is turned back to
an input. When either Relay 2 or Relay 3 is turned on, the AC waveform
input from line L1 or line L2 will cause a 50/60 HZ on-off signal to
appear at the input IN and at the input/output IN/OUT which has been
turned back to an input. The chosen values of the components will depend
on the frequency of the output pulse train and on the method of detecting
the load LOAD. For example, when the predetermined frequency of the pulse
train that is output at the input/output IN/OUT is chosen to be 10 kHZ,
the values of the capacitors C100, C101, and C102 could
be, for example, C100=C101=0.01 μF and C102=0.1 μF.
However, higher or lower values could also be used. As another example,
when the predetermined frequency of the pulse train that is output at the
input/output IN/OUT is chosen to be 1 kHZ, the values of the capacitors
C100, C101, and C102 could be, for example,
C100=C101=0.01 μF and C102=0.0047 μF.

[0082] FIG. 12 is a schematic diagram of another embodiment of the
diagnostic circuit in which more than one heater load LOAD 1, . . . ,
LOAD N can be sensed. The circuit shown in FIG. 12 is constructed and
operated similarly to the circuit shown in FIG. 11. The differences in
the circuit shown in FIG. 12 include providing the voltage sensing and
signal generation device MICRO2 with multiple inputs IN1, . . . ,
INN that apply their input signals to the micro-controlled A/D
device of the voltage sensing and signal generation device MICRO2, and
providing the circuit with multiple branches that each have a respective
load (LOAD 1, . . . , or LOAD N) connected to one of the inputs IN1,
. . . , INN of the voltage sensing and signal generation device
MICRO2. Only two loads LOAD 1 and LOAD N have been illustrated. However,
it should be understood that any desired number of additional branches,
which each have a load and which are each connected to a respective input
of the voltage sensing and signal generation device MICRO2, could be
provided. The three dots drawn vertically between input IN1, and
input INN are used to represent the possible additional
non-illustrated inputs of the voltage sensing and signal generation
device MICRO2 which would each be connected to a respective
non-illustrated branch with a non-illustrated load.

[0083] The diagnostic circuit has terminals or connection points W, V, and
T for connecting to the loads LOAD 1, . . . , LOAD N (of course
additional terminals or connection points can be provided in accordance
with the actual number of loads). The diagnostic circuit also has
terminals or connection points X, U, and S for connecting to the A/C
lines L1 and L2 of the appliance under test (of course additional
terminals or connection points can be provided in accordance with the
actual number of loads).

[0084] An isolation capacitor C74 could be connected between neutral
N of the appliance under test and DC ground. For example, the diagnostic
circuit could have a terminal with one end of the isolation capacitor
C74 connected thereto and the other end of the isolation capacitor
C74 connected to DC ground. That terminal would then be connected to
the neutral N of the appliance under test to thereby connect one end of
the isolation capacitor C74 to neutral N of the appliance under
test.

[0085] When the predetermined frequency of the pulse train that is output
at the input/output IN/OUT is chosen to be 10 kHZ, exemplary values for
the components R70N, C70N, R71N, R72N, and C71N
in the branch connected to the input INN, exemplary values for the
components R70, C70, R71, D100, D101, R72,
and C71 in the branch connected to the input IN1, and exemplary
values for the components R76, C73, R74, R75, and
C72 in the branch connected to the input/output IN/OUT are as
follows: R70N=R70=R76=10K ohms,
C70N=C70=C73=0.001 μF, R71N=R70=R74=1K
ohms, R72N=R72=R75=200K ohms, and isolation capacitors
C71N=C71=C72=0.01 μF. The diode pairs
D100N/D101N, D100/D101 and D103/D102 are
each connected between the positive DC supply potential +5 V and ground.

[0086] All of the relays, namely, Relay 100, Relay 101, . . . , Relay 101N
are placed in the open state to sense whether the loads LOAD 1, . . . ,
LOAD N are connected. The voltage sensing and signal generation device
MICRO2 is set to the operating mode in which a signal, preferably, a
pulse train of a predetermined frequency is output at the input/output
IN/OUT of the voltage sensing and signal generation device MICRO2. For
each one of the loads LOAD 1, . . . , LOAD N to be detected, either the
pulse train output by the input/output IN/OUT is sensed at the
corresponding input IN1 . . . INN or a change of the voltage
across an appropriate capacitor (C70, . . . , C70N) in the
corresponding branch is sensed. For example, the signal that is input at
the input IN1 of the voltage sensing and signal generation device
MICRO2 enables the micro-controlled A/D device MICRO of the voltage
sensing and signal generation device MICRO2 to detect the load LOAD 1 by
either sensing the pulse train output by the input/output IN/OUT or by
sensing a change of the voltage across the capacitor C70 of about
0.5 Vcc. Likewise, the signal that is input at the input INN of the
voltage sensing and signal generation device MICRO2 enables the
micro-controlled A/D device MICRO of the voltage sensing and signal
generation device MICRO2 to detect the load LOAD N by either sensing the
pulse train output by the input/output IN/OUT or by sensing a change of
the voltage across the capacitor C70N of about 0.5 Vcc. The sensing
is performed in a similar way for each of the loads to be detected.

[0087] After all of the loads LOAD 1, . . . , LOAD N have been detected,
the operating mode of the voltage sensing and signal generation device
MICRO2 is changed such that the input/output IN/OUT is turned back to an
input. Then the AC line voltage input at line L2 via Relay 100 and at
each respective one of the connections to line L1 via one of the Relays
101, . . . , 101N are sensed in a manner similarly to the way that has
been explained with reference to the circuit shown in FIG. 6 and Table
IV.

[0088] Alternately, although not preferred, rather than sense all of the
loads LOAD 1, . . . , LOAD N first in the mode of operation in which the
input/output IN/OUT is an output, and then sense the line voltages from
the lines L1 and L2 at all the inputs IN1, . . . , INN and at
the input/output IN/OUT, it is possible to switch back and forth between
the operating modes. For example, the load LOAD 1 could be first sensed
in the mode of operation in which the input/output IN/OUT is an output,
and then the AC line voltages at the input IN1 and at the
input/output IN/OUT could be sensed in the mode of operation in which the
input/output IN/OUT is an input. This sequence would subsequently be
repeated for all loads, for example, until the load LOAD N is sensed in
the mode of operation in which the input/output IN/OUT is an output, and
then the AC line voltages at the input INN and at the input/output
IN/OUT are sensed in the mode of operation in which the input/output
IN/OUT is an input.

[0089]FIG. 13 is a schematic diagram of another embodiment of the
diagnostic circuit in which only one side relay, namely, relay 10 is
provided. This circuit is used with 110 V AC loads. Such loads typically
have higher impedances compared to the loads used in the circuits shown
in FIGS. 10-12. One example of higher impedance load to be used with the
circuit shown in FIG. 13 is a light bulb having an impedance of 200 ohms.
Of course other higher impedance loads can also be used, such as, for
example, 2K ohms. The circuit includes resistors R80-R85,
diodes D121-D122, and isolation capacitors C80-C81.
The isolation capacitors C80 and C81 isolate the components of
the diagnostic circuit located left of the isolation capacitors C80
and C81 from the Load LOAD and the AC Line L1.

[0090] Another isolation capacitor C82 could be connected between
neutral N of the appliance under test and DC ground. For example, the
diagnostic circuit could have a terminal with one end of the isolation
capacitor C82 connected thereto and the other end of the isolation
capacitor C82 connected to DC ground. That terminal would then be
connected to the neutral N of the appliance under test to thereby connect
one end of the isolation capacitor C82 to neutral N of the appliance
under test.

[0091] The diagnostic circuit has a terminal or connection point Z for
connecting to the load LOAD, and a connection point Y for connecting to
the A/C line L1 of the appliance under test.

[0092] When the predetermined frequency of the pulse train that is output
at the input/output IN/OUT is chosen to be 10 kHZ and when the load LOAD
has an impedance of 2 K ohms, example component values could be as
follows: R80=R81=R82=R83=100 ohms,
R84=R85=10 k ohms, C82=0.001 μF, C83=0.1 μF,
and isolation capacitors C80=C81=0.0047 μF. Of course, it
should be understood that different values could be used.

[0093] The voltage sensing and signal generation device MICRO2 includes an
output OUT to send out a signal that has a high frequency compared to
frequency of the AC signal that is applied at Line L1. Preferably, the
values of the components R80, R81, C80, C81,
R82, and R83, are chosen such that with Relay 10 open and with
an open load LOAD, just enough of the high frequency signal will pass to
the input IN to enable the voltage sensing and signal generation device
MICRO2 to sense the high frequency signal. When the load LOAD is present,
it is in parallel with the return signal path and loads down the high
frequency signal such that the high frequency signal is too small to be
seen at the input. After the load is confirmed, the output is turned off
and the Relay 10 is closed. The input IN of the voltage sensing and
signal generation device MICRO2 is then used to look for a 50/60 HZ
signal confirming that the AC voltage has been applied to the load LOAD
via Relay 10.

[0094]FIG. 14 is a schematic diagram of another embodiment of the
diagnostic circuit in which the output Out is used to excite more than
one load, such as, LOAD 1 and LOAD2 in parallel.

[0095] The diagnostic circuit has terminals or connection points CC and DD
for connecting to the loads LOAD 1, and LOAD 2. The diagnostic circuit
also has terminals or connection points AA and BB for connecting to the
NC line L1 of the appliance under test.

[0096] The voltage sensing and signal generation device MICRO2 has an
input IN2 for sensing the signal injected to the load LOAD 1 from the
output Out. The voltage sensing and signal generation device MICRO2 also
has an input IN1 for sensing the signal that is simultaneously injected
to the load LOAD 2 from the output Out. The sensing is accomplished the
same as described above, but all loads LOAD1, LOAD2 must be confirmed
before any AC signal is applied at Line L1 via Relay 11 or Relay 12.

[0097] Exemplary component values are as follows:
R90-R91-R92-R93-R94-R95-R96-R97=1-
00 ohms, LOAD1=LOAD2=2K ohms, C90=C91=C92=C93=0.0047
μF, and C94=0.1 μF. The diode pairs D123/D124,
D125/D126, D127/D128, and D129/D130 are
each connected between the positive DC supply potential +5 V and ground.
Capacitors C90-C93 serve as isolation capacitors to isolate the
components located to the left of the isolation capacitors
C90-C93 from the loads LOAD 1 and LOAD 2 and from the A/C line
L1.

[0098] Another isolation capacitor C94 could be connected between
neutral N of the appliance under test and DC ground. For example, the
diagnostic circuit could have a terminal with one end of the isolation
capacitor C94 connected thereto and the other end of the isolation
capacitor C94 connected to DC ground. That terminal would then be
connected to the neutral N of the appliance under test to thereby connect
one end of the isolation capacitor C94 to neutral N of the appliance
under test.

[0099] The output impedances must be able to drive the maximum loading and
may require a buffer AMPLIFIER as shown in the embodiment of the
diagnostic circuit in FIG. 15. Once again, the output Out is used to
excite more than one load, such as, LOAD 1 and LOAD2 in parallel. The
voltage sensing and signal generation device MICRO2 has an input IN2 for
sensing the signal injected to the load LOAD 1 from the output Out. The
micro-controlled A/D device MICRO also has an input IN1 for sensing the
signal that is simultaneously injected to the load LOAD 2 from the output
Out. The sensing is accomplished the same as described above, but all
loads LOAD1, LOAD2 must be confirmed before any AC signal is applied at
Line L1 via Relay 13 or Relay 14. Exemplary component values are as
follows: R110-R112-R113-R114-R115=100 ohms,
LOAD1=LOAD2=2K ohms, C110=C111=C112=C113=0.0047
μF, and C114=0.1 μF. Capacitors C110-C113 serve as
isolation capacitors to isolate the components located to the left of the
isolation capacitors C110-C113 from the loads LOAD 1 and LOAD 2
and from the A/C line L1.

[0100] Another isolation capacitor C114 could be connected between
neutral N of the appliance under test and DC ground. For example, the
diagnostic circuit could have a terminal with one end of the isolation
capacitor C114 connected thereto and the other end of the isolation
capacitor C114 connected to DC ground. That terminal would then be
connected to the neutral N of the appliance under test to thereby connect
one end of the isolation capacitor C114 to neutral N of the
appliance under test.

Patent applications by James Kopec, St. Charles, IL US

Patent applications by Robert Alvord, Elmwood Park, IL US

Patent applications by DIEHL AKO STIFTUNG & CO. KG

Patent applications in class Of individual circuit component or element

Patent applications in all subclasses Of individual circuit component or element